The present invention relates to tools for automating the development of applications for computer systems.
During application development, it is quite common for a programmer to move a method from one class to another class. This is typically accomplished by manually moving the method from the source class to the destination class, and then fixing up references within the moved method to be compatible with the destination class. For example, the source instance (referred to as “this”) for the source class can become a parameter in the moved method, and the “source parameter” whose class matches the destination class becomes the destination instance (“this”) in the moved method.
When the method is moved, it is customary to replace the original method in the source class with a forwarding method, so that invoking the forwarding method in the source class causes the moved method to be invoked in the destination class. In this way, references to the original method in the source class are automatically forwarded to the moved method in the destination class.
However, using a forwarding method can be tricky because of a simple problem: the source parameter (which becomes “this” in the destination class) may be null. If the forwarder is constructed by simply converting the source parameter into the destination instance as described above, a problem may arise because the destination instance (“this”) in the destination class can never be null. Hence, if the source parameter is null, and the original method in the source class performs some action based on the null value of the source parameter, the moved method in the destination class may not perform the same action.